In high-voltage, high-amperage electrical transmission lines, fuses are used for protection against current overloads. Such fuses are typically incorporated in devices known as “cut-out boxes.” A cut-out box is a substantially rectangular structure, one side of which comprises a replaceable fuse element. As depicted in FIGS. 1 and 2, the lower end of the fuse element is typically rotatably attached to the cut-out box, while the upper end engages a spring-loaded contact. As shown in FIG. 2, the fuse element can be opened by rotating it outward, using a ring or “eye” attached to the fuse, and then removed by lifting its rotatable lower end from its cradle.
When a cut-out box fuse is removed for inspection and/or replacement, the open side of the cut-out box must be jumpered so that the transmission of electrical current is not interrupted. This is a difficult and hazardous operation that requires at least two workers to connect both ends of the jumper across the cut-out box. Standard jumpers usually incorporate a tension coil spring to provide a secure contact with the cut-out box on either end, and this requires stretching the jumper between its contact points, often using a “hot stick” to stretch the jumper.
Examples of stretchable coil spring jumpers are disclosed in the U.S. patents of Steinmayer et al. (U.S. Pat. No. 2,347,851), deMontmollin (U.S. Pat. No. 2,728,056), Curtis (U.S. Pat. Nos. 2,689,944 and 2,728,055), and Larson et al. (U.S. Pat. No. 6,359,229). These designs have within the coil spring a flexible wire conductor that provides the bypass path around the fuse for the electrical current. But these stretchable jumpers have two major drawbacks. First, the operation of stretching the spring-tensioned jumper across the cut-out box is awkward and difficult to perform, especially in high-voltage lines where gloved jumper handling is not permitted and a “hot-stick” must be used. Second, since the bypass wire connector must be flexible enough to stretch out with the surrounding coil spring, the gauge of the bypass wire is severely limited, and such flexible wire connectors are not rated above 100 Amps.
The present invention overcomes these difficulties by providing a cutout box fuse bypass jumper than can safely be installed and removed by a single worker and that bridges the fuse terminal contacts with a heavy-gauge, high-amperage coupling conductor, suitable for currents above 100 Amps.